Flavio C. Cruz

Optical frequency combs generated by four-wave mixing in optical fibers for astrophysical spectrometer calibration and metrology.

Optical frequency combs generated by multiple four-wave mixing in short and highly nonlinear optical fibers are proposed for use as high precision frequency markers, calibration of astrophysical spectrometers, broadband spectroscopy and metrology. Implementations can involve two optical frequency standards as input lasers, or one standard and a second laser phase-locked to it using a stable microwave reference oscillator. Energy and momentum conservation required by the parametric generation assures phase coherence among comb frequencies, while fibers with short lengths can avoid linewidth broadening and stimulated Brillouin scattering. In contrast to combs from mode-locked lasers or microcavities, the absence of a resonator allows large tuning of the frequency spacing from tens of gigahertz to beyond teraHertz.

The infrared absorption spectra and normal coordinate analysis of 13CH3OH, 13CD3OH, and 13CD3OD

Abstract The infrared absorption spectra of the gas-phase 13C-methanol isotopomers, 13CH3OH, 13CD3OH, and 13CD3OD, were measured in the wavenumber region between 400 and 4000 cm−1, at instrumental resolutions of 4 and 0.12 cm−1. The fundamental vibrational wavenumbers were assigned from the spectra with the aid of a normal coordinate analysis using the valence force constants recently determined for the gas-phase 12C isotopomers. Using the fundamental wavenumbers of both 12C and 13C-methanol isotopomers, we obtained a new set of force constants for the methanol molecule by a simultaneous least-squares adjustment to a total of 67 observed wavenumbers.

External power-enhancement cavity versus intracavity frequency doubling of Ti:sapphire lasers using BIBO

We report on continuous-wave second harmonic generation of near infrared Ti:sapphire lasers using room temperature critically phase-matched, angle-tuned BIBO (bismuth triborate, BiB(3)O(6)) crystals, placed both in an external power enhancement cavity and inside the laser resonator. In the first case we generate 70 mW of single-frequency radiation at 423 nm for 330 mW of input power at 846 nm. For intracavity frequency doubling we achieve 690 mW at 423 nm for 7.3 Watts of the Ti:sapphire laser pump power at 532 nm, representing a conversion efficiency of 9.5% from 532 to 423 nm. These tunable blue-violet systems are particularly attractive for laser cooling and trapping of alkaline-Earth atoms.

New fir laser lines and frequency measurements from optically pumped13CD3OH3

We report the discovery of 57 new fir laser lines from13CD3OH molecule optically pumped by a waveguide CO2 laser of 300 MHz tunability. For all lines, precise frequency offset measurements between the CO2 line center and the center of the absorbing13CD3OH line were performed using the transferred Lamb-Dip technique. We have also measured directly the frequency of seven FIR laser lines by heterodyning with already known laser lines. We present a complete list of all known laser lines (134) and frequency measurements (24) for this molecule.

CHD/sub 2/OH optically pumped by a waveguide CO/sub 2/ laser: new far-infrared laser lines from the CD/sub 2/ wagging vibrational mode

For the first time, a wide tunability waveguide CO/sub 2/ laser was used to pump the CHD/sub 2/OH molecule for the generation of new FIR laser lines with a large offset. Optoacoustic signals associated with the infrared absorbing transitions of the CD/sub 2/ wagging vibrational mode served as a guide for finding new laser lines. All lines were characterized in wavelength, relative polarization, intensity, optimum pressure of operation, and precise offset measurements.

Efficient 1 GHz Ti:sapphire laser with improved broadband continuum in the infrared.

We demonstrate a 1 GHz prismless femtosecond Ti:sapphire ring laser that emits 890 mW for 7.6 W of pump power over a continuum extending from 585 to 1200 nm at -20 dB below the maximum. A broadband continuum is obtained with the net cavity group delay dispersion having -50 to 100 fs2 oscillations from 700 to 900 nm. Further broadening is obtained by use of a slightly convex cavity mirror that increases self-phase modulation. Approximately 17% (75%) of the intracavity (output) power is generated in single pass through the crystal, outside the cavity bandwidth, and concentrated in the low-gain IR from 960 to 1200 nm.

Two-photon Doppler cooling of alkaline-earth-metal and ytterbium atoms

The possibility of laser cooling of alkaline-earth-metal atoms and ytterbium atoms using a two-photon transition is analyzed. We consider a {sup 1}S{sub 0}-{sup 1}S{sub 0} transition with excitation in near resonance with the {sup 1}P{sub 1} level. This greatly increases the two-photon transition rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that for calcium, for example, two-photon cooling can be used to achieve a Doppler limit of 123 {mu}K. The efficiency of this cooling scheme and the main loss mechanisms are analyzed.

Laser spectroscopy of calcium in hollow-cathode discharges

We investigated the use of hollow-cathode discharges for high-resolution and high-sensitivity spectroscopy, using atomic calcium. Spectra with sub-Doppler resolution of Cai transitions at 423 (resonant), 610, 612, 616, 645, 657 (intercombination), and 672 nm were obtained by optogalvanic saturation spectroscopy in lamps filled with argon (0.6 and 2.5 Torr) and krypton (0.6 Torr). A Doppler background that is due to velocity-changing collisions, which may severely limit the resolution, can be greatly reduced by the choice of buffer gas. Sub-Doppler linewidths comparable with those achieved in atomic beams have been obtained, making a properly chosen hollow-cathode lamp a convenient tool for high-resolution spectroscopic experiments, providing wavelength references for laser frequency tuning. The sensitivity of optogalvanic detection and the excitation of most electronic levels by the discharge make these lamps attractive also for investigating weak and excited level transitions with the use of a simple experimental setup.

Characterization of new FIR laser lines from CHD/sub 2/OH

In this work, we report new optically pumped far-infrared (FIR) laser lines from CHD/sub 2/OH. A waveguide CO/sub 2/ laser of wide tunability (290 MHz) was used as pump source, and a Fabry-Pe/spl acute/rot open cavity was used as a FIR laser resonator. Optoacoustic absorption spectra were used as a guide to search for new FIR laser lines. We could observe 15 new laser lines in the range from 116.4 to 401.4 /spl mu/m. The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred Lamb-dip technique was used to measure the frequency absorption transition both for the new and previously reported laser lines.

Diode laser and Fourier transform spectroscopy of the13CH3OH C-O stretching mode

In this work we present high resolution Doppler limited absorption spectra measurements of the C-O stretching mode of13CH3OH, obtained from diode laser spectroscopy, and the Fourier Transform spectrum obtained at 0.12 cm−1 resolution. By using these data and previously known spectroscopic information, we determined the frequency and the J quantum number for the multiplets of the P and R(J) branches of the C-O stretching fundamental band. Infrared transitions in coincidence with emission lines of the regular CO2 laser and some of its isotope parents are pointed out.